Product category:
Gears, brakes, couplings and engines
News Release from: Eriks UK | Subject: Gearbox repair services
Edited by the Engineeringtalk Editorial
Team on 18 February 2004
Industrial gearboxes - repair or
replace?
There are tens of thousands of helical and worm gearboxes currently helping to keep UK industry moving; but what happens when they fail?
There are tens of thousands of helical and worm gearboxes currently helping to keep UK industry moving But as manufacturing and processing industries are put under increasing pressure to improve efficiency, those gearboxes can represent a serious cost liability
This article was originally published on Engineeringtalk on 9 Jul 2008 at 8.00am (UK)
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Lean operation means that there is little spare capacity if a mechanical element fails, and in this situation maintenance managers can very quickly be faced with their nemesis - spiralling costs due to unplanned downtime.
In this pressurised environment, the choice between whether a gearbox should be repaired or simply replaced can make a significant financial impact on a company's bottom line profits.
The decision however is not a straightforward one, John Woodcock Product Manager for Gearboxes and Motors at Wyko Industrial Services advises on this decision every day and explains here which is the right decision and why.
When a gearbox failed 15 years ago, there was normally a spare on the shelf and another production line with spare capacity to take over while repairs were made.
The troubled unit would be replaced between shifts and sent for a rebuild as a matter of course, while normal production schedules would absorb the downtime.
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This is no longer the case; deliveries are tight, production speeds are high and more often than not, continuous.
Downtime can now be very expensive and the decision has to be made quickly whether to repair or just replace a unit outright.
The first criterion is always cost versus time; a decision can be made quickly here if there is a breakdown that is causing expensive unplanned downtime.
The question in this situation is down to simple availability; if a replacement is available more quickly than a repair can be made then it is provided.
When advanced age, rarity or size dictates that a replacement is not directly available, then a repair is the only option.
Other clear decisions can be made on most gearboxes in standard reduction sizes under 3kW or with an output torque of up to 800Nm.
This area of the market has seen the largest price drop over the last ten years and the product has effectively become a commodity.
Units are sealed for life and do not have oil top-up facilities, drain plugs or breathers.
Life spans are 3 to 5 years with average usage and when a unit fails or gives signs of failing it is never cost effective or practical to repair, it can simply be replaced.
At the other end of the scale, large gearboxes are normally repaired.
"Large" can be defined loosely in terms of weight or output torque rating, ie any unit weighing over 5t or with an output torque above about 20kNm.
Depending on the access situation, a unit of up to 15t can be removed and repaired.
Gearboxes larger than this are rare and tend to be dismantled on site.
Catastrophic failure is rare in very large gearboxes, although with poor maintenance it can happen - with spectacular and often dangerous results.
The decision to repair or replace is therefore in the balance from around 3kW or 800Nm up to around 20kNm, this represents around 60% of the helical and worm gearboxes currently in use.
Knowing what to do is therefore important for the majority of personnel with maintenance responsibility.
The most urgent requirement for customers who have identified a potential problem is always for information on their options.
The first in making this decision is therefore to find out what has gone wrong.
Complete failures are less common because gearboxes tend to become noisy and stop operating smoothly when there is a problem, this provides an opportunity to either test oil for metallic inclusions or substitute it during a routine maintenance window and send it to a repairer for a report.
When a gearbox comes in for repair, it is stripped down and inspected to identify the cause of the excessive noise, reduced performance or breakdown.
The seals, lubricant, gear teeth and bearings are all inspected.
Finding the cause of a problem is an important step because it may be a simple job to rectify and the unit may only require a good clean and a set of replacement seals and bearings.
In this case it will almost definitely cost less than a replacement, the decision can be made quickly and the work carried out quickly and easily.
A gearbox that has not been removed at the first signs of trouble or has suffered a complete failure is likely to have damaged gears and/or failed bearings.
As soon as any metallic element becomes detached from the bearing or the gears, it is thrown into the moving parts with the lubricant and quickly causes sever wear damage.
In this instance the gears are inspected and their condition assessed before a recommendation is made.
The condition of the different sizes of gears and their availability is important here as small gears can be economically replaced or new ones cut, usually at a cost lower than that of a replacement gearbox.
When both smaller and larger gears are damaged this often marks the crossover point of economical repair, particularly if there are no direct gear replacements available from stock.
It is always advisable to replace gears in pairs and most repairers (Wyko included) will not replace single gears unless the customer requests it or they are very large items and one is in excellent condition - although this is a rare occurrence.
Avoiding or more commonly "extending" the time before a decision to repair or replace a gearbox is always preferable.
The life of most gearboxes can easily be extended through good maintenance practice.
A large proportion of failures are caused by the wrong type of lubricant being used, over and under filling with lubricant and the lack of regular maintenance checks.
Checks can be carried out quickly using vibration-based condition monitoring equipment or simple oil analysis services.
Shock loading is the other common cause of premature failure and is common in conveying and mixing applications where the majority of general industrial gearboxes are used.
Electrical soft starts; variable speed drives and mechanical torque limiters of various types can be used avoid this.
Clutches and couplings are usually fitted between the motor and the gearbox on larger units and at the output shaft of combined gearmotor units.
Wyko Industrial Services offers a complete repair or replace service for helical and worm gearboxes of any size, from fractional kilowatt sizes up to 25t or more.
Collection from site and a condition report is provided free of charge.
As a supplier of new replacement gearboxes Wyko also offers a choice of units from many of the worlds leading manufacturers and keep comprehensive stocks of standard sizes for next or same day delivery. Request a free brochure from Eriks UK ...
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